751
FXUS66 KPQR 060955
AFDPQR
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PORTLAND OR
255 AM PDT WED AUG 6 2025
SYNOPSIS
UPPER-LEVEL TROUGHING AND A WELCOME AUGUST RAIN
THIS MORNING WILL GIVE WAY TO BUILDING HIGH PRESSURE AND A
WARMING AND DRYING TREND THROUGH EARLY NEXT WEEK. CONTINUED
BELOW-NORMAL TEMPERATURES THROUGH THE WORKWEEK WILL STEADILY
RISE TO HAZARDOUS LEVELS BY SUNDAY AND MONDAY.
SHORT TERM...NOW THROUGH FRIDAY NIGHT
A WEAK SURFACE LOW
CONTINUES TO FILL AS IT MOVES BENEATH AN UPPER-LEVEL LOW NORTH
OF VANCOUVER ISLAND. A PAIR OF SURFACE FRONTS EXTENDING TO THE
SOUTH OF THE LOW HAS BROUGHT OVERCAST SKIES AND LIGHT RAIN TO
THE REGION EARLY THIS MORNING, AS FAR EAST AS THE I-5 CORRIDOR
AS OF 2 AM PDT, AND WILL CONTINUE TO SPREAD EASTWARD THROUGH
DAYBREAK. RAIN WILL TRANSITION TO A MORE SHOWERY DISTRIBUTION
THROUGH THIS MORNING PER LATEST CAM GUIDANCE, WITH DECREASING
SHOWER COVERAGE THROUGH TONIGHT AND ONLY ISOLATED LINGERING
SHOWERS IN AREAS OF HIGHER TERRAIN BY THURSDAY MORNING. WHILE
INSTABILITY WILL BE HIGHER TO THE NORTH CLOSER TO THE UPPER LOW,
A FEW RUMBLES OF THUNDER CANNOT BE RULED OUT THIS AFTERNOON AND
EVENING, WITH A 10-20% CHANCE OVER THE SOUTHERN WASHINGTON AND
FAR NORTHERN OREGON CASCADES.
THE MAIN STORY WITH THIS ONGOING SYSTEM WILL BE POTENTIALLY
SIGNIFICANT MID-SUMMER RAINFALL AMOUNTS. THE ARRIVING AIRMASS
IS ABNORMALLY MOIST, WITH FORECAST PRECIPITABLE WATER OF NEARLY
1.5" ACROSS MUCH OF THE REGION EARLY THIS MORNING; IF THIS
FORECAST IS VERIFIED BY THE 12Z KSLE UPPER AIR LAUNCH, IT WOULD
REPRESENT A RECORD HIGH VALUE FOR THE DATE PER SPC SOUNDING
CLIMATOLOGY. THE RELATIVELY WEAK FORCING ASSOCIATED WITH THE
FIZZLING OCCLUDED LOW AND FRONTS MEANS ACTUAL RAIN AMOUNTS WILL
BE WELL BELOW THESE PW VALUES, BUT TRUE WETTING RAINS OF 0.25"
OR MORE REMAIN FAVORED ACROSS NORTHERN PORTIONS OF THE FORECAST
AREA. THE HIGHEST TOTALS EXCEEDING 0.5" ARE EXPECTED IN THE
HIGHER TERRAIN OF THE WILLAPA HILLS, NORTHERN OREGON COAST
RANGE, SOUTHERN WASHINGTON CASCADES, AND THE MT. HOOD VICINITY,
WHILE OTHER AREAS ALONG THE COAST, IN THE CASCADES AND FOOTHILLS
NORTH OF SANTIAM PASS, AND AT LOWER ELEVATIONS NORTH OF SALEM
WILL SEE 0.1-0.5". INTERIOR PORTIONS OF LANE COUNTY REMAIN THE
LEAST LIKELY TO SEE HIGHER ACCUMULATIONS OF RAINFALL, WITH MOST
LIKELY TOTALS OF 0.05" OR LESS.
DRY WEATHER RETURNS THURSDAY NIGHT THROUGH FRIDAY, AS RISING
HEIGHTS ALOFT AND BUILDING SURFACE HIGH PRESSURE OVER THE
NORTHEAST PACIFIC BEGIN TO FAVOR A WARMING TREND. AFTER A NUMBER
OF DAYS WITH BELOW-NORMAL TEMPERATURES, AFTERNOON HIGHS WILL
AGAIN APPROACH SEASONAL VALUES IN THE 80S ACROSS INLAND VALLEYS
AND 60S TO 70S ALONG THE COAST BY FRIDAY. -PICARD
LONG TERM...SATURDAY THROUGH TUESDAY
THE MAJOR PATTERN SHIFT
WILL CONTINUE THIS WEEKEND INTO NEXT WEEK AS HIGH-AMPLITUDE
UPPER-LEVEL RIDGING BUILDS OVER THE PACIFIC, AND THE WARMING
TREND CONTINUES AT THE SURFACE. TEMPERATURES WILL CONTINUE TO
RISE ABOVE NORMAL THROUGH THE PERIOD, APPROACHING HAZARDOUS
VALUES BY SUNDAY AND MONDAY, BEFORE THE PATTERN BEGINS TO
DEAMPLIFY AND SHIFT WESTWARD AWAY FROM THE REGION ON TUESDAY.
AFTERNOON HIGHS ARE LIKELY (75-95% CHANCE) TO EXCEED 90 DEGREES
ACROSS INTERIOR VALLEYS BOTH SUNDAY AND MONDAY. CONFIDENCE
REMAINS HIGH THAT TEMPERATURES WILL PEAK ON MONDAY, WHEN SOME
LOCATIONS MAY SEE THEIR FIRST TRIPLE-DIGIT TEMPERATURE OF THE
YEAR, WITH 35-75% CHANCES OF REACHING 100 DEGREES ALONG THE
WILLAMETTE VALLEY. DEWPOINTS IN THE LOW TO MID 60S WILL
ADDITIONALLY MAKE CONDITIONS FEEL NOTICEABLY HUMID EACH
AFTERNOON, WHILE OVERNIGHT TEMPERATURES MAY FAIL TO FALL BELOW
60-65 DEGREES BOTH SUNDAY AND MONDAY NIGHTS, MOST LIKELY ACROSS
THE NORTHERN AND CENTRAL WILLAMETTE VALLEY, THE LOWER COLUMBIA
AND COWLITZ VALLEYS, THE PORTLAND/VANCOUVER METRO, AND ALONG
THE COLUMBIA GORGE. THIS LACK OF SUFFICIENT OVERNIGHT COOLING
CAN RAISE THE CUMULATIVE HEAT STRESS AND ELEVATE THE RISK FOR
HEAT ILLNESS, RESULTING IN AREAS OF MAJOR HEATRISK. RESIDENTS
OF THE AFOREMENTIONED AREAS SHOULD THEREFORE BEGIN TO PLAN FOR
THIS PERIOD OF HAZARDOUS HEAT. -PICARD
AVIATION
CURRENTLY AS OF 09Z WEDNESDAY, MVFR/IFR CONDITIONS
ALONG THE COAST AND VFR CONDITIONS INLAND AS A FRONTAL BOUNDARY
PASSES THROUGH THE AIRSPACE. EXPECT THESE DETERIORATED
CONDITIONS TO PERSIST ALONG THE COAST THROUGH THE TAF PERIOD,
WITH A POTENTIAL OF DROPPING TO LIFR AT TIMES (20-40% CHANCE FOR
LIFR CONDITIONS MOSTLY BEFORE 00Z THURSDAY). INLAND, CONDITIONS
WILL LIKELY DROP TO MVFR BY 13-15Z WEDNESDAY AND PERSIST UNTIL
00-03Z THURSDAY. CHANCES FOR MVFR CONDITIONS INLAND RANGE FROM
30-70%, WITH HIGHEST TO LOWEST CHANCES FROM NORTH TO SOUTH. ALL
INLAND TERMINALS SHOULD IMPROVE BACK TO VFR BY 00-03Z THURSDAY.
RAIN SHOWERS WILL BEGIN TO TAPER OFF BY 18Z WEDNESDAY FOR THE
COAST AND BY 00Z THURSDAY INLAND. OTHERWISE, EXPECT SOUTHERLY
WINDS THROUGHOUT THE AIRSPACE TO SHIFT SOUTHWESTERLY AS THE
FRONTAL BOUNDARY PASSES (SHIFTING SOUTHWESTERLY AROUND 00-06Z
THURSDAY). INLAND TERMINALS WILL SEE WINDS BELOW 10 KT AND
COASTAL TERMINALS WILL LIKELY SEE WINDS AROUND 10 KT WITH GUSTS
UP TO 20 KT DURING THE AFTERNOON.
PDX AND APPROACHES...CURRENTLY VFR BUT EXPECT CIGS TO GRADUALLY
LOWER AS A FRONT MOVES THROUGH THE AIRSPACE. WHILE LIGHT RAIN
HAS ALREADY BEGUN, EXPECT MVFR CIGS TO DEVELOP BY 13-15Z
WEDNESDAY. WINDS WILL ALSO INCREASE TO AROUND 8 KT OUT OF THE
SOUTH WITH THE ARRIVAL OF THE FRONT. MVFR AND RAIN SHOWERS WILL
PERSIST THROUGH THIS MORNING, IMPROVING BACK TO VFR BY 00-03Z
THURSDAY AS SHOWERS DIMINISH. ~HALL
MARINE
A FRONTAL SYSTEM CONTINUES TO MOVE THROUGH THE WATERS,
BRINGING INCREASED SOUTHERLY WINDS. BUOY OBSERVATIONS CURRENTLY
SHOW WIND GUSTS UP TO 15 TO 20 KT. EXPECT 10 TO 15 KT WINDS WITH
AREAS OF GUSTS TO 20 KT TO CONTINUE THROUGH THE LATE MORNING,
ESPECIALLY CLOSER TO SHORE. CANNOT RULE OUT AN ISOLATED GUSTS TO
25 KT OR TWO, BUT NOT EXPECTED TO BE WIDESPREAD OR FREQUENT.
SEAS WILL BE GENERALLY UNAFFECTED WITH THIS SYSTEM AND REMAIN
NORTHWESTERLY AT 4-6 FT. THESE CONDITIONS WILL PERSIST THROUGH
TODAY. WEDNESDAY NIGHT INTO THURSDAY MORNING, WINDS WILL WEAKEN
AND SHIFT BACK TO NORTHWESTERLY. BY THURSDAY NIGHT, WINDS WILL
INCREASE ONCE AGAIN AND BRING GUSTS UP TO 20 KT FOR THE SOUTHERN
AND CENTRAL WATERS THROUGH FRIDAY AND INTO THE WEEKEND.
~HALL/MUESSLE
PQR WATCHES/WARNINGS/ADVISORIES
OR...NONE.
WA...NONE.
PZ...NONE.
WWW.WEATHER.GOV/PORTLAND
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